The present invention relates to a technique for injecting fuel by opening and closing a fuel supply path formed between a valve element and its valve seat in a fuel injector, the valve seat being driven by the application of an electrical current to coils of the fuel injector.
In an electromagnetic fuel injector (hereafter simply referred to as an injector), a plunger to which a valve element is attached is withdrawn from a valve seat by an electromagnetic force (electromagnetic attraction force) generated by a coil provided in the injector, in which current flows, whereby fuel is injected. When the electrical current flowing in the coil is stopped, the electromagnetic attraction force decays, and the plunger is pressed back by the force of a return spring in the valve closing direction. Thus, the valve of the injector is closed. In an injector of the above-mentioned type, the valve is required to immediately respond to an opening demand or a closing demand without a time delay in order to attain a wide dynamic range of fuel injection. The dynamic range refers to a range in which a linear relationship exists between the fuel injection amount and the valve opening time width, and is expressed by the ratio of the maximum injection amount to the minimum injection amount.
Conventionally, in order to improve the rise time characteristics of the valve opening operation, the following method has been adopted. That is, a high voltage is generated by providing a voltage set-up circuit, and a large current is caused to flow in an injector coil for a short time by applying the generated high voltage to the coil. For example, Japanese Patent Application Laid-Open 241137/1994 discloses a fuel injection control device in which a voltage set-up circuit is provided in a drive circuit for driving an electromagnetic fuel injection valve, and a voltage of 70 V, which is obtained by boosting a voltage of 12 V obtained from an external power source, using the provided voltage set-up circuit, is applied to a drive coil of the electromagnetic fuel injection valve.
In the above fuel injection control device, the excitation current for the drive coil is controlled so that a target value of the excitation current is set as a high value at an initial valve opening time in which a valve element is operated from a closed valve state to a valve opening state (early period in valve opening and during a process of opening the valve), and a low target value of the current is realized by on/off controlling of the drive coil during a valve open hold period in which the valve element is held at in the open state. Thus, the valve opening response is improved by controlling the excitation current for the drive coil at a high target value, and by controlling the excitation current at a low target value during the valve open hold state. In this way, the wasting of power is avoided, and heat generation is suppressed.
Japanese Patent Application Laid-Open 326620/1996 discloses an electromagnetic fuel injection valve in which two coils A and B are provided, and current is caused to flow in the two coils A and B for a preset period after the start of current flow in the coils during valve opening operations. Further, after a preset period, current flowing in the coil A is stopped, and current flows in only the coil B. In the above electromagnetic fuel injection valve, by causing current to flow in both of the two coils A and B for a preset period after the start of current flow in the coils, a strong magnetic flux can be generated and quick valve opening operations can be performed. Further, since a valve element can be held in an open valve state by a necessary and minimum force produced by only one of the two coils during the valve open hold period, a quick valve closing operation can be performed. Moreover, since a large current flows in the coils only at the time of valve opening, heat generation in the injection valve can be suppressed.
Furthermore, in the fuel injection control device disclosed in Japanese Patent Application Laid-Open 241137/1994, a detector for detecting the fuel feeding pressure (fuel pressure) is provided, and a high target value of the excitation current, or the control period for which the excitation current flows at the high target value, is adjusted, based on the fuel pressure defected by the defector. Thus, deterioration in the injection performance of the electromagnetic fuel injection valve, due to changes in the fuel pressure, is avoided.
In the fuel injection control device disclosed in Japanese Patent Application Laid-Open 241137/1994, in which only one coil is provided in the fuel injection valve, the valve element is controlled by the one coil from the start of valve open operations to the end of valve opening operations (valve closing) through holding of a valve open state.
It is necessary to decrease the current flowing in a coil in order to reduce heat generation or power consumption in the fuel injection valve. However, to obtain a sufficient magnetomotive force for holding a valve open state with a small coil current, it is necessary to increase the number of coil turns. On the other hand, since the rise time of the coil current should be made small to improve the response in valve opening, a greater increase in the voltage applied to the coil is required as the number of coil turns is increased. That is, the fuel injection control apparatus disclosed in Japanese Patent Application Laid-Open 241137/1994 has a structure which contradictory has characteristics relative to attaining both a quick response in valve opening and a low power consumption for the valve open hold period, if the same coil is controlled.
Further, since the above-mentioned voltage set-up circuit is expensive, and since insulation measures for the high voltage are necessary, the production cost is increased by adopting such a voltage set-up circuit. Therefore, in order to reduce the production cost, it is desirable to operate an injector with a lower voltage, and it is even more desirable to operate an injector with a battery voltage of 12 V, thereby eliminating a need for a voltage set-up circuit, if possible. Moreover, if an injector is driven by a lower voltage, fewer measures for securing its safety are required, and the maintenance or the adjustment of the injector becomes easier.
In the electromagnetic fuel injection valve disclosed in Japanese Patent Application 326620/1996, the structure and electromagnetic characteristics for each of the coils A and B are not disclosed. In providing two coils, securing a high response in the valve opening operation impedes the objective of holding a necessary and minimum magnetomotive force, and stably holding a necessary and minimum magnetomotive force causes a limitation on the attainment of a high response during the valve opening operation. Therefore, in accordance with this disclosed arrangement of two coils, it is difficult to attain a quick response of the valve opening operation, that is, largely to increase the valve element attraction force, which will be required in the future.
Thus, a first object of the present invention is to provide an electromagnetic fuel injection valve in which the response in driving a valve element from a closed valve state to a valve opening state is improved, and in which the valve opening state can be held stably and with a low power consumption.
A second object of the present invention is to provide an electromagnetic fuel injection apparatus having a wide dynamic range and a low power consumption.
A third object of the present invention is to provide an internal combustion engine in which stable operation can be maintained with a low fuel injection amount.
A fourth object of the present invention is to provide a fuel control method which can realize high response characteristics with a low power consumption.
To attain the first object, the present invention provides an electromagnetic fuel injection valve for injecting fuel by opening/closing a fuel supply passage, including a valve seat, a valve element for opening/closing the fuel supply passage formed between the valve seat and the valve element, and drive means having at least one coil, for driving the valve element, wherein the drive means includes a first magnetomotive force generating means using the at least one coil, and a second magnetomotive force generating means, the first magnetomotive force generating means and the second magnetomotive force generating means being composed so that the first magnetomotive force generating means generates and raises a magnetomotive force at a larger rate of change in time in comparison with the second magnetomotive force generating means.
An electromagnetic fuel injection valve according to the present invention, for injecting fuel by opening/closing a fuel supply passage, includes a valve seat, a valve element for opening/closing the fuel supply passage formed between the valve seat and the valve element, and drive means having at least one coil for driving the valve element, wherein the drive means includes at least one first coil and a second coil of which the number of turns is larger than that of the first coil.
In the above electromagnetic fuel injection valve, the wire diameter of the first coil is larger than that of the second coil.
Further, an electromagnetic fuel injection valve according to the present invention, for injecting fuel by opening/closing a fuel supply passage, includes a valve seat, a valve element for opening/closing the fuel supply passage formed between the valve seat and the valve element, and drive means having at least one coil, for driving the valve element, wherein the drive means includes at least one first coil and a second coil, the first coil and the second coil being composed so that if the same voltage having a rectangular waveform is applied to the first and second coils, the rise time of the magnetomotive force generated in the second coil will be longer than that in the first coil, a saturation value of current flowing in the second coil being smaller than that in the first coil.
To attain the second object, the present invention provides a fuel injection apparatus for injecting fuel by opening/closing a fuel supply passage, which includes an electromagnetic fuel injection valve having a valve seat, a valve element for opening/closing the fuel supply passage formed between the valve seat and the valve element, and drive means having at least one coil for driving the valve element, and control means for operating the electromagnetic fuel injection valve by controlling current flowing in the coil, wherein the drive means includes a first magnetomotive force generating means using the at least one coil and a second magnetomotive force generating means, the coil and the second magnetomotive force generating means generating a magnetomotive force in the same direction in which the force generated in the coil and the force generated in the second means strengthen each other at an initial valve opening time at which the valve element is driven from a closed valve state to a valve opening state, the coil raising the magnetomotive force at a larger rate of change in time in comparison with the second magnetomotive force generating means, and wherein the current flowing in the coil is stopped during a valve opening hold period for which a valve opening position of the valve element is held by the magnetomotive force generated by the second magnetomotive force generating means.
Further, a fuel injection apparatus according to the present invention, for injecting fuel by opening/closing a fuel supply passage, includes an electromagnetic fuel injection valve having a valve seat, a valve element for opening/closing the fuel supply path formed between the valve seat and the valve element, and drive means having at least one coil, for driving the valve element, and control means for operating the electromagnetic fuel injection valve by controlling current flowing in the coils, wherein said drive means includes at least one first coil and a second coil, the first coil and the second coil generating a magnetomotive force by causing current to flow in the first coil and the second coil in the same direction in which the force generated in the first coil and the force generated in the second coil strengthen each other at an initial valve opening time at which the valve element is driven from a valve closing state to a valve opening state, the first coil raising the magnetomotive force at a larger rate of change in time in comparison with the second coil, and wherein the current flowing in the first coil is stopped during a valve opening hold period for which a valve opening position of the valve element is held by the magnetomotive force generated by current flowing in the second coil.
To attain the third object, the present invention provides an internal combustion engine into which fuel is injected by opening/closing a fuel supply passage, which includes a fuel tank, a fuel pump for feeding and pressurizing the fuel from the fuel tank, an electromagnetic fuel injection valve for injecting the fuel pressurized by the fuel pump, which injection valve has a valve seat, a valve element for opening/closing the fuel supply passage formed between the valve seat and the valve element, and drive means having at least one coil for driving the valve element, and control means for determining fuel injection timing and a necessary fuel injection amount injected from the electromagnetic fuel injection valve and for operating the electromagnetic fuel injection valve by controlling current flowing in the coil, wherein said drive means includes a first magnetomotive force generating means using the at least one coil and a second magnetomotive force generating means, the coil and the second magnetomotive force generating means generating a magnetomotive force in the same direction in which the force generated in the coil and the force generated in the second means strengthen each other at an initial valve opening time at which the valve element is driven from a closed valve state to a valve opening state, the coil raising the magnetomotive force at a larger rate of change in time in comparison with the second magnetomotive force generating means, and wherein the current flowing in the coil is stopped during a valve opening hold period for which a valve opening position of the valve element is held by the magnetomotive force generated by the second magnetomotive force generating means.
Further, an internal combustion engine according to the present invention, into which fuel is injected by opening/closing a fuel supply passage, includes a fuel tank, a fuel pump for feeding and pressurizing the fuel from the fuel tank, an electromagnetic fuel injection valve for injecting the fuel pressurized by the fuel pump, which injection valve has a valve seat, a valve element for opening/closing the fuel supply passage formed between the valve seat and the valve element, and drive means having at least one coil for driving the valve element, and control means for determining fuel injection timing and a necessary fuel injection amount from the electromagnetic fuel injection valve and for operating the electromagnetic fuel injection valve by controlling current flowing in the coil, wherein said drive means includes at least one first coil and a second coil, the first coil and the second coil generating a magnetomotive force by causing current to flow in the first coil and the second coil in the same direction in which the force generated in the first coil and the force generated in the second coil strengthen each other at an initial valve opening time at which the valve element is driven from a closed valve state to a valve opening state, the first coil raising the magnetomotive force at a larger rate of change in time in comparison with the second coil, and wherein the current flowing in the first coil is stopped during a valve opening hold period in which a valve opening position of the valve element is held by the magnetomotive force generated by current flowing in the second coil.
In the above fuel injection apparatus or internal combustion engine, reverse current flows in the first coil for a preset period, after which the current flowing in the first coil is stopped, and reverse current is again caused to flow in at least one of the first coil and the second coil for a preset period at the end of a fuel injection demand signal.
In the above fuel injection apparatus or internal combustion engine, at least one of a fuel pressure detector for detecting the pressure of fuel fed to the electromagnetic fuel injection valve and a voltage detector for detecting the voltage applied to the first coil is provided, and at least one of a relation between timing for stopping current flowing in the first coil and fuel pressure and a relation between timing for stopping current flowing in the first coil and the voltage applied to the coils is stored in storage means in the control means, and timing for stopping current flowing in the first coil is determined, based on an output from the detector and the relation.
Further, a method of injecting fuel by opening/closing a fuel supply passage with a valve element of an electromagnetic fuel injection valve, including first magnetomotive force generating means and second magnetomotive force generating means, which is driven by a magnetomotive force generated by using the first magnetomotive force generating means and the second magnetomotive force generating means, the fuel supply passage being formed between the driven valve element and a valve seat against which the valve element is seated, the method comprising the steps of: generating a magnetomotive force with at least one coil used as the first magnetomotive force generating means and with the second magnetomotive force generating means in a force direction in which the force generated in the coil and the force generated in the second means strengthen each other at an initial valve opening time at which the valve element is driven from a closed valve state to a valve opening state; raising the magnetomotive force in the coil at a larger rate of change in time in comparison with that of the second magnetomotive force generating means; and stopping the current flow in the coil during a valve opening hold period for which the valve opening position of the valve element is held by the magnetomotive force generated by the second magnetomotive force generating means.
Furthermore, a method of injecting fuel by opening/closing a fuel supply passage with a valve element of an electromagnetic fuel injection valve including first magnetomotive force generating means and second magnetomotive force generating means, which injection valve is driven by magnetomotive force generated by using the first magnetomotive force generating means and the second magnetomotive force generating means, the fuel supply passage being formed between the driven valve element and a valve seat to which the valve element is seated, the method comprising the steps of: generating a magnetomotive force by causing current to flow through at least one first coil and a second coil in a force direction in which the force generated in the coil and the force generated in the second means strengthen each other at an initial valve opening time at which the valve element is driven from a closed valve state to a valve opening state; raising the magnetomotive force in the first coil at a larger rate of change in time in comparison with the second coil; and stopping the current flowing in the first coil during a valve opening hold period for which a valve opening position of the valve element is held by the magnetomotive force generated by the second coil.
In the above method of injecting fuel, the pressure of fuel fed to the electromagnetic fuel injection valve is detected, and if the detected pressure is higher than in a usual state, the period for which current is caused to flow in the first coil is extended.
Moreover, in the above method of injecting fuel, the voltage applied to the first coil is detected, and if the detected voltage is lower than in a usual state, the period for which current is caused to flow in the first coil is extended.
The term xe2x80x9cmagnetomotive forcexe2x80x9d as used in reference to the above-mentioned electromagnetic fuel injection valve, fuel injection apparatus, and method of injecting fuel, refers to a force generating magnetic field, and if a coil is used for generating the magnetomotive force, the force is estimated by a value obtained by multiplying the number of turns N by the current I, that is, Nxc2x7I. The above second magnetomotive force generating means has only to generate a magnetomotive force at a smaller rate of change in time in comparison with the first magnetomotive force generating means, and it includes means for generating an unchanged force, that is, a constant magnetomotive force, which may be provided by, for example, a permanent magnet or a coil in which a constant current continuously flows from a valve opening operation to a valve closing operation.
In accordance with the present invention, a first magnetomotive force generating means for generating a driving force for movement of a valve element from a closed valve state to a valve opening state with a short rise time, and a second magnetomotive force generating means for generating a driving force suitable to hold a valve opening state with a low power consumption, are independently provided. Therefore, it is possible to improve the performance of driving the valve element from a closing stage to an opening state, and reduction of the power consumption for holding a valve opening state, independently.